Conventionally, protection films may be formed on the lens surface of contact lenses, camera lenses, and optical pickup lenses for CD, DVD, etc., for a variety of purposes. Examples of the protection films include an antireflection protection film for preventing light from reflecting off a lens surface, a hard coating protection film for protecting a lens surface from suffering scratches, and a refractive index adjusting protection film for correcting chromatic aberration of a lens substrate. Molding is used as a method for forming such protection films when the shape or the coating condition of a protection film greatly affects the performance of a lens. In molding, a lens substrate is placed in a protection film molding die, a coating to become a protection film is poured into a space between the lens substrate and the protection film molding die, and after the coating is cured, a lens is taken out from the die. Since the shape of the protection film to be formed by the molding is defined by the protection film molding die, it is possible to obtain a protection film having a desired shape and coating.
However, when the molding is used to manufacture a large quantity of protection films, a large number of expensive dies are required. Further, the number of products that can be manufactured per hour also is limited. Thus, the method is not favorable in terms of production cost.
For such problems, pad printing and screen printing have been known as methods for productively forming a protection film on a substrate including a curved surface, such as a lens, at low cost.
A method of pad printing will be described with reference to FIGS. 24A to 24F. First, as shown in FIG. 24A, concave portions patterned on a printing plate 241 in a desired printing pattern are filled with a coating 242. Next, as shown in FIG. 24B, a pad 243 is pressed on the printing plate 241, and as shown in FIG. 24C, the coating 242 is transferred to the pad 243 from the printing plate 241. Thereafter, as shown in FIG. 24D, the pad 243 is moved over an object 244 to be printed. Then, as shown in FIG. 24E, the pad 243 is pressed on the object 244 to be printed to transfer the coating 242 from the pad 243 to the object 244 to be printed, as shown in FIG. 24F. Even when the object 244 to be printed has a bumpy surface shape, by using a flexible pad made of silicone rubber as the pad 243 in this method, the pad 243 can change its shape along the bumpy surface shape, and therefore a favorable printed matter can be obtained.
Patent document 1 discloses a method for forming a protection film on the surface of a lens using pad printing. In Patent document 1, pad printing is used, at the time of manufacturing a colored contact lens, as a method for forming a base layer and a colored layer on the contact lens. That is, after the base layer and the colored layer are pad-printed on a molding surface of an optical part die, the die is filled with a lens material, and by curing the lens material, the colored contact lens is obtained.
Further, Patent document 2 discloses a method for forming a protection film on the surface of a lens using screen printing. In Patent document 2, screen printing is used as a method for coloring a plastic lens. That is, while rotating a plastic lens, screen printing is carried out on the lens using a squeegee having an edge processed to deform in a curved shape substantially identical to the curved shape of the convex surface of the plastic lens so as to obtain the plastic lens on which a colored layer is formed.
Patent document 1: JP 2004-533629 A
Patent document 2: Japanese Patent 3,758,857 B